Radio receiving system for aircraft



Aug. 30, 1932. F. H. DRAKE ET AL RADIO RECEIVING SYSTEM FOR AIRCRAFT 6 sneets -sheet 1 Filed June 12. 1928 gwwznfota;

Filed June 12, 1928 6 Sheets-Sheet 2 Aug. 30, 1932. DRAKE ET AL I 1,874,935

RADIO RECEIVING SYSTEM FOR AIRCRAFT Filed June 12. 1928 6 Sfieets-Sheet 3 Aug. 30, 1932.

F. H. DRAKE ET AL 1,874,935

RADIO RECEIVING SYSTEM FOR AIRCRAFT Filed June 12, 1928 6 Sheets-Sheet 4 1kg 7 IIIH lllllilh a Aug. 30, 1932. F. H. DRAKE ET AL RADIO RECEIVING SYSTEM FOR AIRCRAFT Filed June 12, 1928 6 Sheets-Sheet 5 g 30, 1932- F. H. DRAKE ET AL 1,374,935 7 RADIO RECEIVING SYSTEM FOR AIRCRAFT 6 Sheets-Sheet 6 Filed June 12, 1928 Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE FREDERICK H. DRAKE, OF BOONTON, LEWIS M. HULL, OF MOUNTAIN LAKES, AND WIL- LIAM D. LOUGHLIN, OF BOON'I'ON, NEW JERSEY, ASSIGNORS, IBY MESNE ASSIGN- MENTS, TO RADIO CORPORATION OF AMERICA, 0]? NEW YORK, N. Y., A CORPORATION OF DELAWARE RADIO RECEIVING SYSTEM FOR AIRCRAFT Application filed June 12,

This invention relates to a radio receiving system of the type adapted for use on aircraft such as aeroplanes, dirigibles and the like, and will be hereafter described in connection with an aeroplane installation. An object of the invention is to provide such a radio receiving system fulfilling certain combined requirements for a receiving system of this character, some of the more im )ortant of which may be enumerated as lig itness; compactness; extreme sensitivity; low current drain; resistance to shocks and vibrations, including protection against variation in the control settings due thereto; simplicity of operation; and a non-directional receiving characteristic permitting successful reception of radio beacon or beam transmitter signals as well as of radio telephone signals. Other objects of the invention will appear from the following description.

lVe have invented a radio receiving system which fulfills the foregoing and other requirements of such a system adapted for use on aircraft in a degree which has not been hitherto obtainable, so far as we are aware. This system will now be described in connection with the accompanying drawings in which Figure 1 shows an aeroplane and a diagrammatic representation of one form of radio receiving system installation according to the present invention; Figure 2 is a circuit diagram of one form of radio receiver suitable for use in such a system; Figure 3 is an end view of one construction of such a radio receiver; Figure 4 is a sectional end view thereof; Figure 5 is a side view thereof showing the tubes; Figure 6 is a side view thereof showing the opposite side; Figure 7 is a bottom view thereof, showing the tube sockets; and Figures 811 show details of one suitable form of tube socket for the receiver.

In the case of a radio receiving system which is required to receive signals from a beam transmitter or radio beacon, for example of the crossed coil equi-signal type, it is necessary that the receiving characteristic be substantially non-directional. It has been found that this type of radio beacon is practically useless if the signals are received on any system having directional characteristics.

1928. Serial No. 284,755.

In order to obtain a substantially non-directional receiving system, it is necessary, first, to provide a non-directional collector or antenna. Any collecting structure having appreciable directional characteristics, such as a loop, or a trailing wire which has a horizontal component due to windage, is unsuitable for this purpose. As a suitable non-directional collector we prefer to employ a rigid metal tube or rod which is preferably so ar ranged or mounted as to assume a substantially vertical position when the aircraft is in flight. Such a collector is shown at 1 in Figure 1 and may, for example, suitably consist of a duralumin tube mounted in the fuselage of the aeroplane, and supported therefrom by insulating bushings, 1 1 or, if preferred, a universal joint and pendulum mounting may be employed as the upper support, the lower support being omitted, so that the collector assumes a substantially vertical position, whatever may be the inclination of the plane in the course of normal flying. The

radio receiving set may be located at any convenient point in the aeroplane, as indicated. The antenna terminal 1 of the set is connected to the collector, and the ground terminal 2 is connected to the fuselage or frame of the aeroplane. The output of the set may go either to a suitable beacon indicator, such as a pair of vibrating reeds or other device mounted on the instrument panel, as shown in Figure 1, or to telephone receivers if radio telephone signals are to be received.

In addition to its non-directional properties, such a rigid collector as that described above possesses numerous advantages over the trailing-wire type of antenna which has been heretofore employed. A trailing wire antenna can only be used when the plane is in full flight, and is ordinarily mounted on a reel. It can not be unreeled until the plane is in flight, and it must be reeled in before the plane can alight. Thus if the aeroplane is suddenly forced down, for example, into the water, the antenna becomes useless for either receiving or transmitting signals. More over, in order to make a trailing wire antenna hang as nearly vertical as possible it is ordinarily provided with a heavy weight or fish at its lower end. When an aeroplane is traversing a rough or bumpy area, these weights frequently snap off and are lost, and may produce very serious damage if this occurs over a city. Moreover the weights have a tendency to fly about on the end of the trailing wire and may cause damage either to the aeroplane, its occupants, or to other planes if the plane is flying in formation.

In order to use a collector of the rigid type successfully it is necessary to employ a highly sensitive receiver in connection therewith especially if relatively low frequencies, of the order of say 300 kilocycles, as commonly employed in radio beacon work, are to be received, because of the shortness and small area of. the collector. In order to meet this requirement we have devised and successfully employed a radio receiver such as that shown in Figures 2-11 inclusive, which is here described as an example only of a receiver su1table for use in an aircraft reception system of the type referred to.

This receiver possesses certain novel circuit arrangements and structural and mechanical features, which will now be more particularly described.

Figure 2 is a circuit diagram of one specific form of receiver. This receiver comprises a two-stage radio frequency amplifier including the tubes T and T a detector including the tube T and two stages of audiofrequency amplification including the tubes T and T Tubes T and T are tubes of the so-called screen-grid tetrode type, provided with anodes P, control grids G screen-grids G and cathodes F. The input system of the first tube T comprises variometer L and trimming condenser 0%. The tuned output circuits for the tubes T and T comprise the variometers L in parallel with the fixed condensers C each of which is shunted by a small aligning condenser C Plate potential is supplied to the tubes T and T through parallel feeds including radiofrequency choke coils L and blocking condensers G Each of the variometers L is grounded, and the grids G are negatively biased with respect to the cathodes F of tubes T and T by means of the resistance R The radiofrequency amplifier is tuned by means of the variometers L L which are ganged or mounted on a common shaft, and operated from a single control, as will be described later. When the trimming condenser C and the aligning condensers C are once set for a particular installation, no further adjustment is necessary and all of the tuned circuits tune to resonance together. This arrangement has been found to contribute materially to the lightness of the receiver, the

heavy and bulky gang variable tuning condensers thus being ehminated; and to simplicit of operation, since the receiver is truly sing e control. The amplification characthe amplification at long Wavelengths, by

this arrangement.

The filaments and screen-grid terminals are suitably by-passed to ground by by-pass condensers C since the compact construction of the receiver to be hereafter described makes the elimination of all stray couplings highly desirable.

The detector includes the tube T provided with anode P, grid G, and cathode, F, and having in its grid circuit the grid condenser O and grid leak R A small regenerator coil L may be included in the detector plate circuit if desired, in order to produce regeneration in the detector. Such regeneration may be arranged to make the amplification characteristic of the receiver substantially constant over the wavelength range, compensating for the decreased amplification at short wavelengths due to the inductance tuning, and may also increase the total amplification. In receivers as here described, we have found that it is possible to produce sufficient regeneration in the detector to increase the overall amplification by a factor of, say, about 2, and also to produce a substantially uniform amplification characteristic, without producing instability in the receiver. A filter section, L C C is arranged in the plate circuit of the detector in order to keep radio frequency currents out of the audiofrequency amplifier, this arrangement also being desirable because of the compact receiver construction. The filter condensers C C are connected to ground; and this radio filter is supplemented by the audiofilter resistance R and condenser C5 as shown in order to keep audiocu'rrent in the detector plate circuit from passing through the B supply.

The audiofrequency amplifier includes 1.

tubes T and T This amplifier is of the resistance-coupled type, the coupling system between the detector and the tube T including the resistances R and R and the coupling condenser 4; and he coupling system be- 7-5:-

tween tubes T and T including the resistances R and R and the coupling condenser C The grids G of the detector T and audiofrequency tubes T andT are biased by means of the resistance R in the filament circuit. The output circuit of the second audiofrequency stage includes the choke coil L and by-pass condensers C and 0 It also includes the telephone jack 3. The terminals 1' and 2 are the antennaand ground terminals, respectively, of the re-- ceiver, 1' being connected to the collector, 1. When the receiver is used in connection with vibrating reeds, for example of the already known type for indicating the radio compass course, as explained above, the terminal 4 is connected to the reeds. The terminals 5, 6, 7, 8, 9 and 10 may suitably have applied to them the voltages 135, 45, 6, 4.9, zero (ground) and -9, respectively, as indicated.

In the specific case of the radio receiver as described above, the following circuit constants may be given as satisfactory, these constants being an example only.

L =choke coils approximately 0.1 henries L =variometers approximately 3.2 m. h.

maximum 1.8 m. h. minimum L =0.7 millihenries regenerator coil L =10 millihenries filter coil L =15 henries choke coil C .001 microfarad condensers C .00005 microfarad condensers.

0' .00004 microfarad mica aligning condensers C =.00007 microfarad mica trimming condenser C =.00025 microfarad grid condenser C .01 microfarad coupling condenser C .-,=.5 microfarad by-pass condensers B 6.0 ohm biasing resistance B 1.1 ohm biasing resistance R =2 megohm grid leaks R =.25 megohm coupling resistance R =1 megohm grid leak R =50,000 ohms filter resistance T and T =UX 222 tubes T and T =UX 240 tubes T =UX 112A tube This circuit arrangement, as described, in connection with Figure 2, has been found to possess a number of important advantages. The screen-grid tetrode tubes T and T give high amplification, and the inductively-tuned coupling circuits provide an amplification characteristic which is especially desirable in a compact receiver of this type, since the lower amplification at the short wavelength end of the wavelength range of the receiver tends to offset the effect of stray couplings in producing instability. The use of a regenerative detector is thus possible without causing oscillation of the receiver, and since the regeneration is greater at short wavelengths, the co-operation between the radio frequency amplifier and the detector produces a substantially uniform high amplification over the wavelength range of the receiver. Moreover, the gang variometers can be made much lighter than equivalent gang condensers, which is an important advantage in a receiver for aircraft. The resistance coupled audioamplifier can also be made lighter than a transformer coupled amplifier and is more efficient at the low frequencies which are commonly used to modulate the beacons.

Figures 3-11 inclusive illustrate the structural and mechanical organization of a receiver embodying the above-described circuit. This structure is light, strong, shock-proof,

' the resilient couplings 11 showin vibration-proof, and possesses other advantages which will appear from the following description. The various circuit elements described in connection with the circuit diagram of Figure 2 are designated by the same reference characters.

Figure 3 is an end view of the receiver showing the manner in which the receiver casing 13 is supported from the arms 14 and 15 of the mounting-bracket 12 by means of and cooperating cou ling-engaging cups 11, all of which will be ereafter more particularly described in connection with the three-point shock insulation system. control 24 and cooperating pointer 25 and scale 26'.

Figure 4: is a sectional end view showing the end of the receiver casing 13 removed. The second degree of shock insulation, comprising the resilient couplings 17, is also shown, as well as the tube-damping resilient members 22, one of which is attached to the sub-panel 20 and a cooperating one of which is attached to the hinged closure 13 of the receiver casing 13, and the vibration-proof control arrangement including ratchet 25 and spring paul 26, as will be hereafter more fully described.

Figure 5 is a side view of the receiver with the side closure removed to show the tubes and the gang socket therefor, together with the shock cushions 11 and 17.,

Figure 6 is a View of the opposite side of the receiver from Figure 5, and shows the arrangement of the ganged variometers'already described in connection with Figure 2.

These variometers L are mounted on a common shaft, 23, supportedin bearings 23. Each variometer is enclosed in a separate completely shielded compartment, 27, which compartment is especially constructed so as to be highly conductive in the direction of the strongest electromagnetic field of the variometer. This may be accomplished by making complete conductive connection between all members of a common aluminum shield for the variometer gang.

Figure 7 is a bottom view of the receiver the gang tube socket 16, including the indlvidual sockets 2-1, and the extension arms 19 from which the gang socket is supported by means of the cushions 17.

Figures 8, 9, 10 and 11, are, respectively, top, bottom, side, and sectional views ofa flexible socket 21, Figure 11 being taken on the line AA of Figure 9. These flexible sockets constitute the third degree of shock insulation of the tubes, as will be hereafter described.

Having now described the physical organization of the receiver generally, according to the several figures, certain particular features thereof will now be described more in detail Figure 3 also shows the tuning lit the shield, or bydie-casting in order to point out the manner of cooperation of the several arts referred to.

Figures 3, 4, 5, and 8-11 illustrate the shock-mountinr arrangement employed for the receiver. This shock-mounting includes three degrees of shock insulation, as mentioned above. The first degree. of insulation is obtained by means of the shock cushions 11 which are arranged between the receiverinounting-bracket 12 and the receiver casing 13. (See Figures 3, 4 and 5.) These shock cushions 11 are suitably engaged at each end by the cup members 11, one of which is carried by the receiver casing 13 and a coo erating one of which is carried by an arm 0 the mounting bracket 12, for each cushion member 11, whereby the cushion members are supported by, and constitute an elastic or resilient coupling between, the cup members 11, and through the latter, between the mounting bracket and receiver casing. In the preferred construction six of the shock cushions 11 are employed, two being arranged between the upper bracket members 1414 and the receiver casing 13, and four being employed between the lower bracket members 1515 and the receiver casing 13, so as to produce a three point suspension of each end of the receiver casing 13 from the mounting-bracket The second degree of shock insulation is shown in Figures 4, 5 and 7. The tube sockets for all of the tubes are arranged in'a gang socket 16, which is separated from the receiver casing 13 by means of the shock cushions 17. The latter are located between the gang socket 16 and the supporting-arms or brackets 19 carried by the sub-panel 20 of the receiver casf ing 13, and are held in place by means of bolts 18; the shock cushions 17 being mounted above and below the gang socket 16 at each point of suspension.

The shock cushions 11 and 17 may be constituted by any suflicientlyresilient and selfdamped material, but we have found that cylindrical pieces of sponge or crepe rubber of approximately the shape and size shown in the drawings are well suited for this purpose.

The third degree of shock insulation is built into the individual sockets 21 as shown in Figures 7 and 8 11. Each of these sockets is suitably of the flexible type, as illustrated in Figures 8-11. These sockets comprise an exterior annular member 28 which is attached to the gang socket 16 by means of the exterior flexible lugs 28, and which is attached to the central socket disc 29 by means of the interior flexible lugs 30; thus providing a universal flexible support for the socket disc 29 from the gang socket 16. The holes for receiving the tube prongs, and the contact members, are arranged in the socket disc 29 in'the usual manner.

It will be seen that by this shock insulation system a series of elastic or resilient couthese resilient couplings has a different vibration period, due to the different mass attached thereto, so that the entire shockmounting structure constitutes a sort of mechanical filter for shock impulsesafi'ecting the frame or fuselage of the aero lane.

A further improved element of the receiver structure is the resilient members 22 (see Figures 4 and 5) which are mounted on the subpanel 20 and the hinged receiver closure 13' so as to contact with the tubes, T T T T T at a point above the maximum diameter of the bulbs. The resilientmembers 22 thus serve a dual purpose, since in the first place they act to damp the vibration of the tubes, and in the second place their pressure upon the curved bulbs tends to force the tubes into their respective sockets, thus insuring good contact between the prongs in the tube bases and the sockets, and preventing the tubes from working out of the sockets.

Still another improved feature of the physical organization of the receiver is the means for rendering the receiver controls vibrationproof. Referring to Figures 3, 4 and 6, the common shaft of the gang variometers L is shown at 23, and extends through the receiver casing to the crank 24 by which the receiver is tuned, asshown in Figure 3, a pointer 25 and scale 26 being arranged to cooperate therewith for this purpose. Mounted on the shaft 23 between the variometers and the tuning crank 24 is a fine tooth ratchet 25 (see Figures 4 and 6), which operates in conjunction with spring pawl 26. By this arrangement the tuning control is fixed at any given adjustment, and any residual vibration reaching the receiver from the motor, or other disturbance, does not detune the receiver. This arrangement'is found to be of considerable importance in actual practice, since when the pilot is flying a compass course on a radio beacon he usually has both hands otherwise engaged, and cannot stop to adjust the receiver. When the receiver is provided with a filament rheostat or volume control, we prefer to employ a similar vibration-proof eontrol for these adjustments, so that when the able for use in our receiving system in connection with a non-directional collector of the type described, the invention is not necessarily limited to the particular novel features of the radio receiving set described but extends to a complete radio receiving system for aircraft, as herein set forth.

e claim 1. An electrical amplifier circuit comprising, in combination, a multi-stage radio frequency electrical amplifier including a plurality of tubes of the screen-grid type, said tubes being linked through tuned coupling impedances comprising a fixed tuning condenser and a variable tuning inductance arranged in parallel, whereby the amplification of said radio frequency amplifier is less at short wavelengths than at long wavelengths; and a regenerative detector stage coupled to the last of said radio frequency amplifier stages, said regenerative detector stage including circuit elements of predetermined fixed magnitude efi'ective to produce higher amplification at short wave lengths than at long Wave lengths, whereby the overall amplification of said radio frequency amplifier and detector may be made approximately uniform over the tuningrange of said receiver.

2. A radio receiving set of the type suitable for use in aircraft, and including three degrees of shock insulation interposed between a rigid receiver mounting and the're'ceiver tubes, each of said degrees of shock insulation being constituted by a resilient coupling between masses of different size, and each resilient coupling having a diiferent natural period of vibration.

3. A radio receiving set as claimed in claim 2, wherein one of said resilient couplings resides between a gang socket member and the individual tube sockets thereof.

4. In a radio receiver for use on aircraft, the combination with a support adapted to be rigidly mounted upon the aircraft structure and comprising a frame havin an upper and a lower bracket projecting roin each end thereof, of a receiver, and shock-proof couplings providing a three point support between each end of said receiver and the brackets at the respective ends of said supporting frame.

5. In a radio receiver, a receiver casing in the form of a metallic box having one hinged side constitutinga closure for said box, a partition extending longitudinally of said casing, a sub-base yieldingly supported between said partition and said hinged side of said casing, said sub-base carrying a plurality of sockets for receiving vacuum tubes, and resilient members carried by said partition and saidcover for engaging the vacuum tubes assembly comprising a metal box having a plurality of variometers in said box, a shaft extending longitudinally through said box and carrying the adjustable element of each variometer, and plates extending across said box between adjacent pairs of variometers, the connections between said plates and said box being highly conductive in the direction of the strongest magnetic field established by said variometers.

7 In radio receiving means adapted for stable operation, the combination of a receiver including tubes separated from a rigid receiver mounting by three degrees of shock insulation, circuits including tuning means intercoupling said tubes, and a vibrationproof control means for'said tuning means comprising a member adapted formovement, a ratchet member'connected therewith, and a pawl member cooperating with said ratchet member whereby said control means is held at any given setting until reset.

8. A radio receiver adapted for stable operation including a plurality of thermionic tubes, a receiver mounting, and supporting means for said tubes interposed between said mounting and said tubes, said supporting means for said tubes including three degrees of shock insulation, the degrees of shock insulation each having a difierent natural period of vibration.

In testimony whereof, we aflix our signatures.

FREDERICK H. DRAKE. LEWIS M. HULL. WILLIAM D. LOUGHLIN.

above their sections of maximum diameter,

whereby said resilient members retain the tubes in sald sockets and damp the vibration thereof.

6. In a radio receiver for use on aircraft,

the combination with a metallic casing having one side hinged thereto and a partition extending longitudinallyoi said casing, of tube sockets mounted in said casin between said partition, and said hinged si e of said casing, and a shielded gang variometer assembly mounted onsaid partition at the side thereof opposite said tube sockets, said 

